ideas & ramblings

Lock ‘n roll: a tale of three cartridges

(Originally published in 2019.)

Nearly all video gamers of a certain age are familiar with game cartridges and how to use them: plug a cartridge into your console, turn the console on, and start playing. Less known are the cartridges that were not quite so simple, including a subset that were designed to have other cartridges plugged into them. Let’s take a look back at three of these quirky middlemen to see why the creators of lock-on cartridges bothered with an extra cartridge slot in the first place, how these cartridges took advantage of the games that were plugged into them, and just what each lock-on cartridge’s unique design had to offer gamers.

This is part one of a four part series on the wonders of video game cartridges.

Game Genie

Photo of Game Genie for the NESThe Game Genie was probably the first video game cheat device that your average home console gamer ever encountered. This clever gadget sat between the Nintendo Entertainment System (NES) and standard game cartridges and gave gamers the ability to tweak difficulty levels, jump ahead in a game, or just have fun messing around with things.

For 90s kids, the Game Genie was effectively magic. First, you’d plug one of your game cartridges into the Game Genie. Then, usually with some degree of difficulty (because it was a rather tight fit), you’d wedge the combination Game Genie and game into your console and power the console on. Instead of the game starting up as usual, you’d be greeted with a mysterious screen that prompted you enter nonsensical passwords1. Each password would affect your game in a different way, and no two games used the same passwords.

So, how did Game Genies grant their game wishes? Game Genies—there were versions available for the NES, the Super NES, and the Game Boy, as well as the Sega Genesis and the Game Gear—worked by intercepting communications between the console and game cartridge. Because the inner workings of a game console are ruled by bits and bytes, the relatively simple ability to rewrite data passing from the cartridge to the console was all that was needed for the Game Genie to pull off some incredibly neat tricks.

Screenshot of Game Genie password screen
Game Genie's password entry screen on NES.

Essentially, the password you entered would tell the Game Genie what to do: replace this part of the game’s programming code, change the starting value of that in-memory data, or prevent this part of memory from ever changing. If you plugged in Super Mario Bros. 3, for example, and then used the password LEUXKGAA with your Game Genie, you’d enter World 1-1 with Mario already sporting his iconic Raccoon Mario power-up.

The first Game Genie was developed in the late 1980s by a British company called Codemasters. Although it was the first cheat cartridge for a video game console, it wasn’t the first cheat cartridge ever made. Cheat cartridges originated in the home computer market, with 1986’s Action Replay being the earliest example23. Given Codemaster’s origins as a developer for Commodore computers, it’s very likely that the creators of Game Genie drew their inspiration from the Action Replay.

At any rate, after a few years of flying high—including an extensive legal battle with Nintendo—Game Genies vanished just as optical discs took over as the primary storage medium for home consoles.

Super 3D Noah's Ark

Photo of Super 3D Noah's Ark cartridge
Super 3D Noah's Ark, ready to have another cartridge attached.

The early 1990s were a prolific time for grey-market Christian-themed video games. Most religious games of that era were shoddy imitations of more popular games with Bible themes sprinkled haphazardly throughout. As a result, only few of these games are of any interest to us4. Super 3D Noah’s Ark, though, was strange enough to be worthy of our attention.

First of all, the game that Super 3D Noah’s Ark based its gameplay on was, bizarrely enough, id software’s über-violent first-person shooter Wolfenstein 3–D. Rather than wandering the dark corridors of Nazi fortresses, players would instead run through Noah’s Ark putting unruly animals to sleep with food.

The switch from Nazis to Bible stories came to be in a rather roundabout way. When Wolfenstein 3–D was ported to the Super NES a few years after its original release on the PC, Nintendo demanded id make substantial changes to the content of the game. As originally programmed, the game was far too violent to suit Nintendo’s vision of itself as the console of choice for younger video gamers and, of course, the parents who inevitably were the ones to actually buy the consoles. id complied, but they weren’t happy about it. So, in an adorable act of subversion, id licensed their game engine to Wisdom Tree5, an unlicensed maker of subpar religious-themed video games, and Wisdom Tree simply re-skinned the game and called it their own. Rather than playing as a gun-toting American soldier, players found themselves controlling a slightshot-wielding version of Noah, subduing unruly goats & sheep rather than mowing down Nazis.

Comparison of Wolfenstein 3–D with Super 3D Noah's Ark
Left: Wolfenstein 3–D — Right: Super 3D Noah's Ark

Having miraculously landed one of the most impressive game engines of the time, Wisdom Tree now had to find a way to publish Super 3D Noah’s Ark, but it wouldn’t be easy. In the 80s and 90s, Nintendo had a strict set of content policies that games had to follow—that same rules that had so infuriated id software—and these policies included a complete ban on any religious content. Despite the ban, there was a small cottage industry of religious video game developers anxious to cash in on the video game craze by selling games to well-meaning parents seeking to insert some of their values into this newform of entertainment. However, these developers all faced the same technical challenge: Nintendo consoles wouldn’t play cartridges unless they contained one of Nintendo’s proprietary Checking Integrated Circuit “CIC) security chips. Games that circumvented the CIC chips of the original NES were somewhat common6, but Super 3D Noah’s Ark was the sole unlicensed game for the Super NES.

One look at Super 3D Noah’s Ark’s novel lock-on cartridge tells the whole story. Unhappy that their CIC chip for the NES could be subverted, Nintendo built a stronger version of the chip for the Super NES. In order to circumvent the CIC chip, Super 3D Noah’s Ark required that you first plug an ordinary licensed Super NES game into the top of its cartridge and then plug Super 3D Noah’s Ark into the console. Clever engineering allowed the CIC signals to pass through the unlicensed cartridge and up into the licensed one, making the console believe that a licensed game was being played.

This was a masterstroke of creative problem solving, and despite looking a little unusual, the lock-on strategy did what it needed to. It may seem surprising that this strategy didn’t see more use7, but the Super NES never attracted much attention from the religious gaming industry. Bootleg Bible-themed NES games continued to be released even after official releases for the system dried up8.

Sonic & Knuckles

Photo of Sonic & Knuckles cartridge with Sonic the Hedgehog 3 attached
Sonic & Knuckles with Sonic the Hedgehog 3 attached.

Last but certainly not least is Sonic & Knuckles, a 1994 release for the Sega Genesis that completed the original Sonic the Hedgehog series. Unlike the other two cartridges we’ve looked at, Sonic & Knuckles is perfectly functional on its own, offering six levels of classic platforming action. At first glance, it doesn’t even look like anything special—it’s cart is a bit odd, but nothing like the other two we’ve talked about. But, instead of a top label like ordinary Genesis cartridges, this one sported a flip-top lid, and beneath that, a slot for another Genesis cartridge to slide in.

This lock-on cartridge had quite a few tricks up its sleeve. Depending on which game you added, you’d see one of three things. When most Genesis games were plugged in, players would be able to play variations on Sonic the Hedgehog 3’s “blue sphere” bonus levels. Sonic & Knuckleswould read the second cartridge’s identifier, and then vary the layout of the bonus levels on that. Players could experiment with different games to find different sets of levels; for example, if plugging in _ToeJam & Earlgave a set of levels that was too difficult, maybe the player might have more luck after plugging in Altered Beast.

Things got more interesting with Sonic the Hedgehog 2. Screenshot of Knuckles in Sonic the Hedgehog 2 Sonic & Knuckles would read the data off the Sonic 2 cartridge and splice the character Knuckles in place of Sonic, with all of his abilities from later games intact. This meant that players could play with a fresh new character in a game that was released years before that character was even invented. It was a brilliant idea that went a long way toward making Sonic & Knuckles feel like a good value.

The real star of the show, however, was Sonic the Hedgehog 3. Plugging in this game (which had been released a mere eight months earlier9Screenshot of Knuckles in Sonic the Hedgehog 3 would give you Sonic 3 & Knuckles, a new experience that flowed smoothly from the levels of Sonic the Hedgehog 3 to those of Sonic & Knuckles. This combination is considered the “real” version of the game, and its unusual release strategy is the famous result of tight time constraints—Sega released the first half of the game as soon as it was ready, and released the second half as this lock-on cartridge later in the year10.

Despite making gamers have to purchase two games to get the full Sonic the Hedgehog 3 experience, the lock-on gimmick was novel enough to feel worth it. Unfortunately, Sonic & Knuckles was the only lock-on cartridge of its type to see the light of day.

It's a Lock

Video game cartridges were a really remarkable medium11, full of surprises and offering plenty of opportunity for creative additions as time went on. These cartridges barely scratch the surface of an intricate and fascinating history of oddball hardware hacks and middlemen intended to push home consoles beyond their limits and providing unique experiences for gamers. In part two, we’ll take a look at lock-on cartridges’ bigger siblings: video game cartridges that contained distinct video game systems of their own.

This is part one of a four part series on the wonders of video game cartridges. Continue on to learn about systems in cartridges.

Many thanks to my patient and helpful wife, Nathalie, for copyediting this article.


  1. Hackaday has a short article on how the Game Genie worked that’s worth reading. The basic idea is that part of the passwords identified a part of the game’s memory, and the rest of the code tells the Game Genie what to do with it: either always keep it frozen at a particular value, or conditionally change it to a particular value depending on its current value. It’s both simple and brilliant. ↩︎

  2. The first dedicated cheating device was the Action Replay, released for the Commodore 64 in 1986. Much like the Game Genie, it went on to spawn a series of variants for different computers and consoles over the course of the next decade. ↩︎

  3. A predecessor to dedicated cheat devices were hardware peripherals like the Multiface, which offered enthusastic tinkerers unprecedented access to the innards of their computers. These let users do just about anything to the software that was running on their computer, including cheat. ↩︎

  4. If you don’t mind foul language and potty humour, there’s a YouTube series called The Angry Video Game Nerd that has humourously reviewed quite a few of these games over the years. ↩︎

  5. Some people consider the story of id software licensing their engine to Wisdom Tree as apocryphal. It’s hard to verify one way or the other, but the fact is included in 2004’s Masters of Doom (page 121). However it happened, Super 3D Noah’s Ark is definitely built on top of the Super NES version of Wolfenstein 3–D. ↩︎

  6. The most famous publisher of unlicensed NES games is Tengen (owned by Atari), but they got around Nintendo by illegally reverse engineering the NES CIC chip using documents that had been filed by Nintendo with the US Patent Office. Camerica offers a more honest (and interesting example): their strategy for bypassing the lock-out chip was to send it glitchy pulses of electricity, temporarily knocking the chip out of commission. ↩︎

  7. Little Red Hood, a bootleg game considered by many to be one of the worst games available on the NES, also used this sort of lock-on cartridge. ↩︎

  8. Sunday Funday was last game to receive a North American release for the console, at least until resurgence of interest in vintage gaming in the 21st century. ↩︎

  9. Sonic the Hedgehog 3 was released in North America on February 2, 1994, and just 258 days later, Sonic & Knuckles was released on October 18. ↩︎

  10. See the development section of the Sonic & Knuckles Wikipedia article for more details. ↩︎

  11. This is somewhat of a recurring theme here; see my prior article on the history of saved games to learn about how persistent memory was added to video game cartridges via the addition of a tiny button cell battery. There are countless other examples of the brilliance of cartridges that we’ll surely cover here at some point in the future. ↩︎

Image sources